Aromatic diazo compounds having at least two diazo groups in the molecule (hereinafter referred to as "multifunctional diazo compounds") are industrially important as photosensitive agents for forming the photosensitive layer of materials such as lithographic printing plates, screen printing plates, color image formation materials and the like. Heretofore, such photosensitive agents typically uses a condensate (so-called diazo resin) of diphenylamine-4-diazonium salt (or 4-N-phenylaminobenzene diazonium salt) and formaldehyde as a typical compound. Production methods for such multifunctional diazo condensates are described in specifications of U.S. Pat. Nos. 2,679,498, 2,922,715, 2,946,683, 3,050,502, 3,311,605, 3,163,633, 3,406,159, and 3,277,074.
Thereafter, many patents on such multifunctional diazo compounds have been published. For example, Japanese Patent Publication 49-45323/1974 and Japanese Patent Publication Laid-open 62-156656/1987 propose the use of a special compound such as 4,4'-bismethoxymethyl-diphenylether as a condensation agent for diphenylamine-4-diazonium salt in place of formaldehyde. Furthermore, Japanese Patent Publication Laid-open 2-3049/1990 finds that hexamethoxy-methyl-melamine is satisfactory as such a special condensation agent.
In order to enhance the water solubility of multifunctional diazo compounds, Japanese Patent Publication 40-26623/1965, Japanese Patent Publication Laid-open 1-102457/1989, Japanese Patent Publication Laid-open 1-245246/1989, and Japanese Patent Publication Laid-open 3-163549/1991 describe the use of a carbonyl compound having carboxyl or sulfonic acid group in place of formaldehyde. Multifunctional diazo compounds described in the above patents have diphenylamine-4-diazonium salt as a basic structural unit, but multifunctional diazo compounds having 4-N,N-dialkylaminobenzene diazonium salt as a basic structural unit are also effective as photosensitive agents for use in photosensitive compositions. Typical patents on such compounds are Japanese Patent Publication 1-57332/1989 and Japanese Patent Application 153295/1991 (filed on Jun. 25, 1991).
As described above, a variety of multifunctional diazo compounds have heretofore been developed, and these compounds are broadly classified by applications into water-soluble diazo compounds and organic solvent-soluble diazo compounds. Water-soluble multifunctional diazo compounds are primarily used as photosensitive agents for use in screen printing plates and colored image formation material (e.g. color proof films), whereas organic solvent-soluble diazo compounds are often used for lithographic printing plates.
Water-soluble multifunctional diazo compounds present the following two common important problems that have yet to be solved.
1) Improvement of the method of separating the desired water-soluble multifunctional diazo compound from the reaction mixture after the completion of the synthesis reaction. In a method that has heretofore been published, the reaction mixture is poured into an organic solvent (such as isopropyl alcohol) in which the water-soluble multifunctional diazo compound is less soluble to precipitate the desired diazo compound, which is then separated and dried to a powder. This method requires recovery of the organic solvent used and, as a result, tends to increase pollution of the waste water.
2) The production of the photosensitive composition containing a diazo compound. Water-soluble multifunctional diazo compounds are usually supplied as powders. Because they tend to decompose when they adsorb moisture, commercial diazo compounds are stored in an extremely dry condition. The dried powder tends to scatter in the production of photosensitive compositions containing the diazo compounds, resulting in pollution of the work place and adverse effects on the workers' health. Therefore, a liquid or paste multifunctional diazo compound has been in demand.